Occultation sensing of an atmosphere (e.g., the earth's atmosphere) is a well-developed and highly useful technique. Briefly, occultation sensing involves passing light through an atmosphere's limb and then viewing the light at a remotely-located sensor (e.g., a sensor in orbit in or beyond the atmosphere). The sensed light is analyzed to determine the properties of the occulting atmosphere.
The output of occultation sensors can be used to infer an atmosphere's temperature profile as a function of altitude based on either an extinction or refraction profile of the light passed through the atmosphere's limb. In both techniques, light from a single source (e.g., a star) is sensed after that light passes through the atmosphere. The light is typically sensed using a sensor mounted on an orbiting satellite or a moving spacecraft.
The disadvantage of using the extinction technique is that one must know the concentration profiles of the absorbing gases in the atmosphere (e.g., CO2). However, it is difficult to know a concentration profile with a great deal of precision since it can vary with altitude, atmospheric conditions, seasonal conditions, etc., thereby affecting the precision of a determined extinction profile.
To determine the refraction profile, a sensor's orientation, movement, and direction of movement must be monitored so that measurements can be appropriately adjusted. However, it is extremely difficult to control/measure satellite or spacecraft motion with sufficient precision to make the refraction technique viable. That is, typical sensor platform motions include many oscillating and non-linear components that produce uncertainties exceeding performance capabilities of measurement systems and processing schemes.